<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        #div{
            height:40vw;
            width: 40vw;
            background: blue;
            text-align: center;
            line-height: 40vw;
            color: #fff;
        }
    </style>
</head>
<body>

    <!-- 
        750px 设计稿时
        @vm:7.5vw;
     -->
    <div id="div">11111</div>
</body>
</html>